Exemplary embodiments of the present invention relate to a (built-up) cam unit for the rotationally-fixed and axially displaceable arrangement on a main camshaft body of a camshaft (which is built-up or is to be built-up). Moreover, exemplary embodiments of the present invention encompass a camshaft having a main camshaft body and a cam unit disposed on the main camshaft body in a rotationally-fixed and axially displaceable manner, in accordance with the main claim. Furthermore, exemplary embodiments of the present invention encompass a camshaft module which supports, in an at least partially peripherally closed bearing device, a built-up camshaft having a drivable main camshaft body and at least one cam unit mounted on the main camshaft body in an axially displaceable and rotationally-fixed manner, in accordance with the main claim.
German Patent Document DE 10 2004 011 586 A1 discloses a valve train for an internal combustion engine, which comprises at least one camshaft on which at least one cam carrier is disposed in a rotationally-fixed and axially displaceable manner. Formed between the camshaft and the at least one cam carrier are means for applying an axial clamping force which is used to fix the at least one cam carrier axially in the bearing receptacle. The proposed cam carrier comprises at least one cam, on which at least two different cam tracks are formed, and is surrounded for bearing purposes by a camshaft bearing fixed to the cylinder head. The proposed cam carrier consists substantially of a total of three components: an axial main body including integrated cams on both sides and a track profile pressed in each case on the two free ends of the main body.
Exemplary embodiments of the present invention are directed to a cam unit (hereinafter also referred to as a built-up cam unit), whereby on the one hand the cam unit, and in corresponding developments also a (built-up) camshaft supporting such a (built-up) cam unit as well as a corresponding camshaft module comprising such a (built-up) camshaft are to be optimized in terms of manufacturing costs and functional requirements placed on such a (built-up) cam unit.
According to exemplary embodiments of the present invention, a cam unit is further divided into individual, prefabricated individual components such that these individual components can be manufactured in a simplified manner and can be designed optimally in terms of their technical requirements, in particular through different material properties. Furthermore, the modular design of such a “built-up” cam unit for a “built-up” camshaft should simplify the assembly of a camshaft module with such an assembled (built-up) camshaft in terms of the installation of the camshaft in the at least partially peripherally closed bearing receptacle (e.g., bearing block or bearing/ladder frame or the like) of the camshaft module.
In accordance with exemplary embodiments of the present invention, a cam unit (in terms of a so-called “switchable cam” having at least two different cam track profiles allocated to a common cam follower) for the arrangement on a main camshaft body of a built-up camshaft in a rotationally-fixed and axially displaceable manner comprises at least one main tubular sleeve body and at least one cam element disposed on the main sleeve body in a rotationally-fixed and non-displaceable manner. In accordance with the invention, the sleeve body and the at least one cam element are formed as separately produced individual parts. The cam element is advantageously formed of multiple parts and comprises at least two individual disk elements that are disposed axially adjacent to each other, are allocated to a common cam follower and have different cam track profiles (peripheral profiles). Alternatively, the cam element can be formed in one piece, wherein it is contoured on the periphery such that several cam track profiles are formed axially next to each other. In the following description, a cam element is understood to mean a one-piece cam element having several cam track profiles and also each individual disk body of a cam element in multiple parts is designated as a cam element. In one aspect of the invention, a separately produced track element is connected to the main sleeve body of the cam unit. This ensures in a simple manner that the individual components, such as main sleeve body, cam element(s) and track elements, can be produced from different materials or different material compositions of the same material. Furthermore, the properties of the individual components can also be individually improved by way of further, separate processing thereof and these components can be individually adapted and optimized in terms of their respective function. For example, a main sleeve body produced from simple structural steel (e.g., St52-3, 40MnB5, 26MnB5, C60, CF53 or the like) can support a cam element produced from a forged, special and (e.g., inductively) hardened steel or a cam element consisting of a sintered metal. A track element to be connected to the main sleeve body can also be produced from a steel which has been correspondingly further processed (e.g., nitrided) or from a sintered metal and can be connected to the main sleeve body consisting of another steel (or consisting of another material or of another material composition).
In order to correspondingly reduce the manufacturing costs, the separately produced track elements and the main sleeve body (-ies) provided with an inner toothed arrangement are produced from a conventional structural steel. The cam elements are preferably formed to be forged in accordance with a standard production process for built-up camshafts. In order to be able to optimally satisfy the functional requirements placed upon the individual components, the track elements are advantageously formed to be (inductively) hardened and in particular nitrided, whereas the forged cams can be hardened, in particular inductively or in another manner, in a further processing step. The connection between the individually separately produced components to be assembled to form a cam unit can be effected via a press-fit connection, a positive-locking connection, a solder, adhesive or weld connection or any combination of said connection possibilities.
The invention further encompasses a built-up camshaft having a main camshaft body (which can be formed as a whole or in sections to be soft, hardened and/or nitrided) and a cam unit disposed on the main camshaft body in a rotationally-fixed and axially displaceable manner (and also can be formed as a whole or in sections to be soft, hardened and/or nitrided) as was constructed or produced in accordance with preceding embodiments.
Exemplary embodiments of the present invention further involve a camshaft module having a bearing device with bearing receptacles for rotatably bearing the built-up camshaft, wherein the built-up camshaft is of the previously described type.
In the particularly preferred embodiment of the camshaft module, the assembly and bearing of a built-up camshaft are provided in closed bearing blocks or in a so-called closed bearing tunnel. In terms of the invention, such a closed bearing tunnel is understood to mean a bearing receptacle/bearing that is formed to be partially or completely peripherally closed such that assembly of the main camshaft body or the camshaft is only possible by laterally sliding-in the main camshaft body. It is not possible to insert the camshaft transversely to the rotational axis thereof into a corresponding bearing receptacle in the case of such bearing receptacles. Assembling built-up camshafts in a one-piece bearing block or in a one-piece ladder frame or in a closed bearing of a cylinder head cover (monolithic cylinder head cover) or the like is generally extremely problematic owing to the narrow constructional space and the assembly process that is complicated as a result. Conventionally, this problem has generally been avoided by forming the ladder frame or its bearing receptacles as separate components in multiple parts for a so-called “open bearing receptacle” (into which a camshaft can be inserted transversely to the bearing/rotational axis). In other conventional arrangements, the inner diameter of the cam shaft bearing has been extended such that the camshaft could be assembled axially (slid-in laterally) in one piece including the cams and functional elements disposed thereon (so-called tunnel bearing). In the former case, increased production and assembly outlay is generally unavoidable. In the latter case, the increase in the bearing diameter results in increased friction in the valve train and a negative effect, associated therewith, with respect to the required constructional space.
In the camshaft module according to exemplary embodiments of the present invention, the main sleeve body of the cam unit is characterised in that starting from one of the two free ends of the main sleeve body, the outer diameter of the main sleeve body is adapted at least in regions to the inner diameter of the bearing device such that the main sleeve body can be laterally slid into the closed bearing receptacle. In one aspect of the camshaft module of the present invention, the outer diameter of the cam unit is adapted at least in regions to the inner diameter of the bearing device such that a sliding bearing is created between the main sleeve body and the bearing receptacle.